how much hotter do engines get after you shut them

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I've noticed that engines become much hotter once you shut them off. I've had it where I start one up just long enough to back it out of the garage, so it runs 30 seconds. I can feel it 5 minutes after I shut it off and the valve cover is way hotter than it was when I just shut it off. I guess this is just heat soak?
 
Most engines are made entirely from Aluminum these days, which absorbs and dissipates heat better than the old iron engines.
 
I don't think the engine can get hotter as you are no longer adding heat to it. Or at least not at the rate you do while running.

But that heat is radiating throughout the engine. So parts that were cooled by the movement of fluids or air are no longer being cooled, so they pick up that radiated heat.

I.E. individual parts may get hotter, but the engine as a whole is not getting hotter. So while your valve cover may be getting hotter, the exhaust manifold is likely getting cooler as it's heat radiates away.
 
That's just heat soak.

Once the release of energy (heat) from combustion has stopped, the engine block doesn't get any hotter.

Coolant sometimes spikes up a bit because a portion of the volume is stuck in a warm part of the engine, like a water jacket or water passage on a wet manifold. Even then, coolant (water) is an excellent thermal conductor and will dissipate that heat quite quickly.
 
Originally Posted By: javacontour
I don't think the engine can get hotter as you are no longer adding heat to it. Or at least not at the rate you do while running.

But that heat is radiating throughout the engine. So parts that were cooled by the movement of fluids or air are no longer being cooled, so they pick up that radiated heat.

I.E. individual parts may get hotter, but the engine as a whole is not getting hotter. So while your valve cover may be getting hotter, the exhaust manifold is likely getting cooler as it's heat radiates away.



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Combustion heat retained in the engine can't be removed very well with the cooling system shut down. THe old Jag XJ series used to have a cooling fan for the battery box. AS I recall it had a timer. I had several SAABS with cool down timers on the electric radiator fans.
 
Somewhat related, but my fuel and coolant temp gauges need to be fed 5 voltsDC.

I used to have the stock 1930 technology voltage limiter in place, and then replaced it with a solid state unit.

Not only do the gauges not swing wildly anymore with voltage or with radio interference, but the temp gauge does not swing up into the red briefly on a hot restart. Both fuel and temp gauges rise slower to true levels on restart, hot or cold.

I did not expect this hot restart aspect of a solid state voltage regulator. I had hoped for the higher stability and got it, for 1/5 the price of a replacement mechanical voltage limiter.
 
Originally Posted By: DemoFly
That's just heat soak.

Once the release of energy (heat) from combustion has stopped, the engine block doesn't get any hotter.

Coolant sometimes spikes up a bit because a portion of the volume is stuck in a warm part of the engine, like a water jacket or water passage on a wet manifold. Even then, coolant (water) is an excellent thermal conductor and will dissipate that heat quite quickly.


So the heat is just spreading to the most outer portions of the engine?
 
Originally Posted By: javacontour
I don't think the engine can get hotter as you are no longer adding heat to it.


SCIENCE!
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Originally Posted By: motor_oil_madman
Originally Posted By: DemoFly
That's just heat soak.

Once the release of energy (heat) from combustion has stopped, the engine block doesn't get any hotter.

Coolant sometimes spikes up a bit because a portion of the volume is stuck in a warm part of the engine, like a water jacket or water passage on a wet manifold. Even then, coolant (water) is an excellent thermal conductor and will dissipate that heat quite quickly.


So the heat is just spreading to the most outer portions of the engine?

Correct. The centrally located heat (combustion chamber) is spreading to the cold outsides of the engine block and accessories.

Cast Iron and Aluminum are thermal conductors.
 
The above is generally true especially for regular cars; but there are exceptions when the critical components depend on active cooling to dissipate the heat.

So the answer to your question depends on what your definition of "engine" is. Exactly where you are measuring a temperature, there are definitely components that gets hotter after shutdown. If you are defining the engine as the combustion chamber where it's 2000 degrees or whatever, then yes it's not going to get hotter than 2000 degrees, if there are no more burning of fuel in there.

Real Life common examples that show this :
Turbo cars, especially modified ones, utilize idle timers to let the turbo cool down before completely shutting down.

Race cars also have to take a cool down lap, they don't just shut it down right at finish. In F1, when they can't take a cooldown lap, they have to stuff blowers onto all the intakes so the heatsoak doesn't damage parts.

Or, if you have a video projector, when you turn it off, the fan keeps going for some extra minutes to prevent the lamp and components from overheating from the residual heat
 
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Many up to date turbo cars have electric oil and coolant pumps...wich after you shut off your car go in action and start to cool down for example turbo bearings...so that traped oil there would not cook there
 
Originally Posted By: Olas
They don't get hotter, they just don't cool as quickly.



If internal heat is quickly being pulled to the outside, creating the illusion of a warmer engine post shutdown, they are cooling more quickly.
 
When the engine is running, heat is absorbed by the coolant and pumped to the radiator and released into the surrounding environment. When the engine isn't running, the heat instead flows to the coolest components because of the law of entropy. The valve covers are much cooler than the block so heat flows to the valve covers. Also, heat is rising from the exhaust system. The valve covers may be getting hotter but the other areas are getting equally cooler. Overall the engine does not get hotter when it's off... that'd be impossible.
 
Originally Posted By: Kamele0N
Many up to date turbo cars have electric oil and coolant pumps...wich after you shut off your car go in action and start to cool down for example turbo bearings...so that traped oil there would not cook there


Actually good designs also use basic thermodynamics and heat transfer to keep coolant flowing to a high spot without any pumps.
 
Originally Posted By: javacontour
I don't think the engine can get hotter as you are no longer adding heat to it. Or at least not at the rate you do while running.

But that heat is radiating throughout the engine. So parts that were cooled by the movement of fluids or air are no longer being cooled, so they pick up that radiated heat.

I.E. individual parts may get hotter, but the engine as a whole is not getting hotter. So while your valve cover may be getting hotter, the exhaust manifold is likely getting cooler as it's heat radiates away.



^ This. The heat is just in a different place than when running.
 
I had an off track excursion in my old Neon on a track day which I was running high 230's with the heater on. So after a sudden stop and sitting for a while shut off, I limped it off the track and later checked my scangauge. It had recorded a max coolant temp of 268F. I didn't notice it boiling over so I don't know how accurate that number is, but that's what the ECU saw at some point.

Also if you look up how a barn of wet hay catches on fire, heat transfer isn't always as intuitive as you would think! Common sense would say its impossible, but its common knowledge that it happens.
 
It's a very vague question because as previously mentioned, because "engine" and "hotter" need to be defined more accurately.

Can engine coolant temperatures increase after shutdown? Absolutely. The engine's parts can store thermal energy that no longer has a path for rejection, and that thermal energy goes into the coolant, which no longer has an effective path of rejection, and it temporarily builds.

Anyone who has done drag racing knows how this whole thing works. Plenty of times I have watched intercooler, engine coolant, and even transmission fluid temps creep higher than during the run itself and require a cooldown before running again.

As already noted, it's not "the engine" getting hotter. It's hotter components with stored thermal energy discharging that energy into places that can no longer effectively discharge it, and overwhelming those pathways to discharge through other pathways it normally would not take. i.e., heat energy working its way past stagnant coolant in cylinder head jackets to the valve covers.
 
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